| What is odour? |
| What is an odour threshold? |
| What is odour number? |
| What's the secret of odour busting? |
| What is an odour mask? |
Odour is a chemical or combination of chemicals, which, when carried in air stimulates the olfactory bulb in our nose. On one end of the complexity scale, a smell or odour can comprise of a very simple chemical such as ammonia; i.e. a single chemical that is known to be odorous, whilst on the other end of the scale a cooking smell, say of curry, can actually comprise of several hundred different chemicals (some of which may be very large and complex molecules), which combined give a particular smell sensation. It is for this reason of chemical complexity and smell variety, that there is never an absolute cure for all smells.
It is the concentration (in parts per million ppm or mg/m3) of the smelly chemical in the air at which half of a panel of testers (human noses) can detect the odour and half cannot. Some chemicals are incredibly odourous e.g. Trimethylamine can be smelt at concentrations as low as 0.00021 parts per million or 0.0005 mg/m3. Some other known smelly chemicals have very high odour thresholds e.g. Ammonia 46.8 parts per million or 33 mg/m3
This is a measure of the intensity of an odour. If you take an sample of the smelly air, the 'odour number' of that sample is the quantity of equal volumes of clean odour free air, that have to added to the sample to dilute it down to the odour threshold, i.e. the concentration at which half of a panel of testers can detect it. An odour number can be as low as 2 or 3 and as much as 2 million in the case of some very concentrated industrial odour sources.
What's the secret of odour busting?
There is no secret but there is a lot of know how and capable technology that when correctly applied can be very effective.
In industrial applications, the smell is more often that not, caused by known chemicals that are part of the industrial process. For this reason it is much easier to specify a solution that is ideal for that particular smell. Smells from other sources, e.g. within the home, cars, offices, bars, and restaurants are less specific, therefore the solutions that is used tend to be unspecific, and therefore general deodourisers tend to be used, which are known to be effective across a wide spectrum of different smells. Controlling smells is either achieved by pulling all the air through an air cleaner that has carbon filters so that the smell is physically removed by filtering at a faster rate than it is being produced, or, by applying a substance to the air.
An odour mask is a substance that is generally a pleasant smell that is used to disguise a unpleasant one. The substance is generally sprayed into the air or evaporated from a wick. These perfumes can be effective, but they have a couple of problems. Firstly the masking fragrance can over time become as undesirable as the smell being masked. There have been instances of water companies using masking agents to disguise the smell of sewage works, only to discover that complaints about the smell of sewage get replaced by complaints about the smell of roses. The second problem is that in a enclosed space i.e. a room or building the masking agent can potentially cause discomfort to people with chemical allergies.